EXCLUSIVE: Inside Janet Jackson's Grueling Rehearsals, 65-Pound Weight Loss

On Monday, the 51-year-old singer showed off her slim post-baby body on Twitter, sharing a pic of herself in rehearsals. Our source says Jackson's been rehearsing "almost 15, 16 hours" a day in preparation for her State of the World tour, which kicks off in Lafayette, Louisiana, on Sept. 7.

"It's a grueling schedule but she is up to the task," the source says. "She wants to blow the crowd away. She will be perfection like her brother, Michael. She's all about the showmanship."

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Clearly, Jackson is looking in shape since she gave birth to son Eissa in January.

Hey u guys. I’m so excited for the State of the World Tour. We r in rehearsal mode. See u guys in 1 month! pic.twitter.com/CUIrfbzJ1l

— Janet Jackson (@JanetJackson) August 8, 2017

"She has lost more than 65 pounds and has her pre-baby body back and then some," our source says. "It's possible that she could lose another 10 pounds before the start of the tour."

As for spending time back in Los Angeles after living in London, England -- where her estranged husband, Wissam Al Mana is based -- the source says Jackson is loving being closer to her family.

"She's happy to be back in the states in L.A. where she learned about music and performing with her brothers, and it was important for her to give this experience to her son," the source shares. "She wants baby Eissa to know her family."

Jackson hasn't been shy about being out and about in L.A. She and Eissa visited Kitross Kids, a children's store on Robertson Blvd., on Saturday, a second source tells ET. They played with colorful baby toys while in the store, and the source noted that the singer looked to be in incredible shape.

"Janet was in great spirits," the source says. "She was a very doting mother. She looked amazing. She's slimmed down and ready for her tour."

As for 7-month-old Eissa being on the road with Jackson, our original source says it won't be an issue.

"Eissa is an easy baby," the source says. "He'll be a great roadie!"

NEWS: EXCLUSIVE: Janet Jackson Moves Back to L.A. With Son to Be Near Family, Working on Documentary

Thankfully, Jackson and Al Mana appear to still be on good terms. In May, a source told ET that Al Mana sent his estranged wife a mix of over 100 roses and orchids for her birthday.

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